With recent developments in Graphical User Interface (GUI) environments, a pointing device has come into wide use as a substitute for the keyboard in PC operations. The pointing device moves the cursor to a window, icon or similar visual interface to enable the PC to execute the operation designated by the window or icon.
Conventional pointing devices include those which are independent of PCs, such as a mouse. However, with the widespread use of notebook or similar portable PCs, there has been a demand for a pointing device which is easy to carry along with the PC and which saves space for operation on the go. To meet such a demand, a pointing device of the type that is built into the PC main unit has been developed.
FIGS. 8 through 10 illustrate a conventional pointing device 100 built in the main unit of a PC 110. As shown in FIG. 8, a control button 101 is mounted in a PC housing 111 and protrudes from the keyboard panel so that a user actuates it with his thumb while holding other fingers at home positions.
As depicted in FIG. 9, the control button 101 is composed of a truncated conical stick 102 and a disc-shaped flange 103 which are formed in a single piece of hard rubber. A fulcrum projection 104 on the underside of the flange 103 is loosely fitted in a positioning hole made in a rigid panel 105 so that the control button 101 is rockingly supported on the rigid panel 105.
At four corners around the control button 101, strain gauges or similar pressure-sensitive elements 106a to 106d are disposed. The strain gauges or pressure-sensitive elements 106a to 106d have pressure receiving pieces 107a to 107d held just above the circumferential margin of the flange 103 at four places, respectively. The strain gauges or pressure-sensitive elements 106a to 106d are each connected to a transducer (not shown) for transducing the output of the strain gauges or pressure-sensitive elements 106a to 106d to voltage.
With the pointing device of the above described construction, when the stick 102 is tilted, a tensile force is applied to the pressure-sensitive element pressed by the stick 102 and the voltage corresponding to the tensile force is output from the transducer.
A microcomputer (not shown), which is equipped in the pointing device 100, detects the direction of tilt of the stick 102 by comparing output voltages from the four pressure-sensitive elements 106a to 106d and the angle of tilt of the stick 102 on the basis of a voltage change, and produces and sends out cursor control data to the PC 110. That is to say, the direction and angle of tilt of the stick 102 are used to produce 8-bit positional data in the X and Y directions, which is sent out as part of the cursor control data to the PC 110.
To make the pointing device 100 compatible with a mouse or other tablet pointers, the cursor control data mentioned herein uses the same data format as that of cursor control data that is output from the mouse or similar.
FIG. 7 is a table showing an example of the data format of the cursor control data. Positional data in the X direction of the 3-byte cursor control data is contained at bit positions X0 to X7. Positional data in the Y direction of the 3-byte cursor control data at bit positions Y0 to Y7.
Thus, the conventional pointing device 100 permits controlling movements of the cursor according to the direction and amount of tilt of the stick 102 in the same manner as does the manipulation of the mouse.
The pointing device 100, though capable of outputting 8-bit positional data as the cursor control data, detects the direction and amount of tilt of the stick 102 by the use of only the four pressure-sensitive elements 106a to 106d. Therefore, the pointing device 100 cannot attain high resolution in both of the direction and the amount of tilt of the stick 102 and cannot control the cursor exactly in response to the stick manipulation.
On the other hand, only a limited number of pressure-sensitive elements can be provided in the narrow space defined in the PC housing 111 and an increase in the number of the pressure-sensitive elements would only make circuitry complex and raise the manufacturing costs accordingly.
Further, as shown in FIG. 9, there is a gap 113 between the rocking stick 102 and the PC housing 111. Water, dust or foreign particles may get in the housing 111 through the gap 113 and thus, cause malfunctions of circuit components in the PC housing 111.
As a pointing device with high stick control resolution but free from the above-mentioned problem of the gap 113, a tablet pointer is known that makes use of the principles of operation of a tablet, a digitizer and so forth. This tablet pointer derives positional data from the position on the tablet sheet where it is being pressed, and outputs cursor control data, ensuring accurate detection of the absolute position on the tablet sheet being pressed. By tightly joining the marginal edges of the tablet sheet to the PC housing 111, there will be no gap between the marginal edges of the tablet sheet and the PC housing even during operation.
To form a PC-contained pointing device by mounting the above-mentioned conventional tablet pointer in the PC housing 111, however, the operation area of the tablet sheet needs to be reduced. Thus, the pointing device poses a problem in its operability in the case of continuously moving the cursor, because it is necessary that the tablet sheet be pressed in two or more steps as described below.
FIG. 11(a) shows the case of moving the cursor from a point 0 to (4) via (1), (2) and (3) on a PC screen 112.
The cursor can be moved from the point 0 to (1) on the PC screen 112 by pressing the tablet sheet 107 from a point "0" to (1) with the user's finger, for instance. The tablet pointer calculates absolute positions (x.sub.0, y.sub.0) and (x.sub.1, y.sub.1) of the points "0" and (1) in the X and Y directions and multiplies their difference, i.e., the relative position (X', Y'), by a predetermined constant C to obtain positional data (see FIG. 11(b)).
The PC 110 moves the cursor on the screen 112 according to the cursor control data containing such positional data, so the cursor moves in proportion to the value of relative movement data.
Similarly, continuing the pressing of the tablet sheet 107 to the point (3) via (2), the cursor draws on the PC screen 112 a locus similar to the path of the finger on the tablet sheet 107.
As mentioned previously, however, the tablet sheet 107 needs to be as small as about 3 square centimeters, far smaller than the PC screen 112; consequently, even when the point (4) still remains unreached by the cursor on the screen 112 as depicted in FIG. 11(a), the pressing of the tablet sheet 107 can no longer be effected. The frequent occurrence of such an interruption of the tablet sheet pressing operation makes the cursor control cumbersome.
A similar problem can arise when moving the cursor merely straight for a relatively long distance on the PC screen 112. That is, to move the cursor straight for a long distance on the PC screen 112, it is necessary to repeat pressing of the tablet sheet 107 over a certain distance thereon in the same direction a plurality of times.
A possible solution to these problems is to use a large constant C, but this fails to minutely control the movement of the cursor, and hence also presents the problem of the lack of operability.
Another possible solution is to contain the absolute position on the tablet sheet 107 as positional data in the cursor control data. Unfortunately, this method also encounters, but cannot settle, a problem similar to that in the case of deriving the positional data from the afore-mentioned relative position.